When you're a gadfly, you can flit above the substantive debate, because it's your posture rather than your knowledge of policy that matters most. People who argued with McCain years ago about campaign-finance reform always were shocked by how little he knew about his own signature policy initiative. It's been a long road for McCain to get up to speed on domestic policy, and he's constantly fallen back on one of his greatest hits as a gadfly, his opposition to earmarks.
Gadflies are loners because they spend so much time offending their own side. In his initial primary campaign prior to the 2007 meltdown, McCain staffed up with Bush loyalists — because there were so few McCain loyalists — who didn't understand his appeal. Now, his general-election campaign is rife with former Bush staffers leaking to the press to save their post-McCain campaign reputations. Ah, the agony of the gadfly.